Catalyst components for the stereospecific polymerization of olefins are known in the art. The polymerization of olefins such as propylene is often performed using Ziegler-Natta catalysts which comprise a solid catalyst component such as a magnesium (Mg) dihalide on which a titanium (Ti) compound and an internal electron donor compound may be supported, and optionally an Al-alkyl compound. When high polymeric crystallinity is required, an external donor (for example, an alkoxysilane) may be further required to obtain higher isotacticity. In addition, internal donors such as esters of phthalic acid, including diisobutylphthalate, may be used. The phthalates are often used as internal donors in combination with alkylalkoxysilanes as external donors. This catalyst system often gives good performance in terms of activity, isotacticity and xylene insolubility.
However, one of the problems associated with the use of this catalyst system is the potential health concerns associated with the use of phthalates.
Consequently, many research activities have been devoted to the discovery of alternative classes of internal donors for use in the preparation of catalyst components for propylene polymerization.
Some of the tested catalysts contain donor structures having amido and ester groups. For instance, WO 2006/110234 describes amino acid derivatives, including one carbamate group and one free ester function, that may be used as internal donors. The catalysts generated by these structures have very low activity and sterospecificity in bulk propylene polymerization (Table 2).